Thermal switch mechanism

ABSTRACT

A thermal switch mechanism includes a pair of spaced apart arms. A thermal actuator is mounted on one arm and extends toward the other, with a toggle spring interconnecting the actuator and the other arm. A heater is positioned for selectively heating the actuator so that the actuator selectively will move in opposite directions. A stationary contact is provided on each side of the actuator, which carries a movable contact for engagement with each of the stationary contacts, depending on the direction of movement of the actuator. A screw extends between the arms for setting the distance therebetween to adjust the switch differential. An insulator is normally positioned between the movable contact and one of the stationary contacts and is movable therefrom. A second, normally open switch is interconnected with the insulator. When the insulator is moved from between the movable contact and one of the stationary contacts, the normally open switch is closed.

United States Patent Allison, Jr.

[451 June 27, 1972 [72] Inventor:

[52] US. Cl ..337/102 [51] Int. Cl. ..HOlh 61/02 [58] FleldoiSearch ..337/9l,92,98,100,101,102,

337/112; ZOO/61.19, 156 M [56] References Cited UNITED STATES PATENTS 2,288,640 7/1942 Paulus ..337/92 Summers Taylor ..200/61. 19

Primary Examiner-G. R. Simmons Assistant Examiner-F. E. Bell Attorney-John M. Stoudt, Radford M. Reams, Ralph E. Krisher, Jr., Joseph B. Forman, Frank L. Neuhauser and Oscar B. Waddell ABSTRACT A thermal switch mechanism includes a pair of spaced apan arms. A thermal actuator is mounted on one arm and extends toward the other, with a toggle spring interconnecting the actuator and the other arm. A heater is positioned for selectively heating the actuator so that the actuator selectively will move in opposite directions. A stationary contact is provided on each side of the actuator, which carries a movable contact for engagement with each of the stationary contacts, depending on the direction of movement of the actuator. A screw extends between the arms for setting the distance therebetween to adjust the switch differential. An insulator is normally positioned between the movable contact and one of the stationary contacts and is movable therefrom. A second, normally open switch is interconnected with the insulator. When the insulator is moved from between the movable contact and one of the stationary contacts, the normally open switch is closed.

7 Clalns, 5 Drawing figures BACKGROUND OF THE INVENTION The present invention relates to thermal switch mechanisms. Thermal switches normally include a movable contact carried by a thermal actuator for movement in different directions as the temperature of the actuator varies. Normally one or more fixed contacts are provided to cooperate with the movable contact to control desired circuits, depending on the direction of movement of the actuator. By providing a heater for controlling the changes in temperature of the thermal. actuator such switch mechanism can be used as timers.

Many prior art thermal switch mechanisms, particularly those designed to function as timers have become rather complex. Much of the complexity resulted from attempts to make them less sensitive to ambient temperature variations and to variations in the voltage applied to the heater. Such efforts have not been completely successful. Also, since the movement of the actuator usually is also utilized to control the energization of the heater, such switch mechanisms are basically continuous duty type devices. That is, they continuously repeat their cycle of operation unless some external means is employed to interrupt their operation. In the past such external cycle interruption means has added considerable complexity and cost. This has militated against their use in single cycle operation applications.

One such potential single cycle application is as a control for charging nickel cadmium batteries. Controls for the charging of such batteries need to be of the single cycle type. Also the charging time must be closely controlled and substantially independent of such extraneous factors as variations in the ambient temperature and the voltage applied to the control. For these reasons, among others, controls for such chargers have tended to be rather expensive timer or electronic arrangements rather than thermal switch mechanisms.

SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a new and improved thermal switch mechanism.

It is another object of this invention to provide such a new and improved thermal switch mechanism which is stable and sure in operation and yet is of a simple and inexpensive construction.

It is yet another object of this invention to provide such a new and improved thermal switch mechanism which is substantially insensitive to variations in such factors as ambient temperature and applied voltage.

It is still another object of this invention to provide such a new and improved switch which will automatically inactivate itself after a desired sequence of operation.

The invention, in one form thereof, provides a thermal switch mechanism including first and second spaced apart stationary contacts. A movable contact is biased toward engagement with the first stationary contact and is movable to engagement with the second stationary contact. There is blocking means, normally in a first position preventing engagement of the first stationary contact and the movable contact. The blocking means is manually actuable to a second position allowing engagement of the first stationary contact and the movable contact. There is thermal drive means eflective to disengage the movable contact from the first stationary contact and to engage it with the second stationary contact. Thereafter the thermal drive means is effective to disengage the movable contact from the second stationary contact and return it toward the first stationary contact. The blocking means returns to its first position upon the thermal drive means effecting disengagement of the movable contact and the first stationary contact.

The above mentioned and other features and objects of this invention, as well as the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description, taken in conjunction with the accompanying drawing, wherein:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a thermal switch mechanism for use as a battery charger control and incorporating one form of the present invention, the view being partly broken away;

FIG. 2 is a partial top plan view of the thermal switch mechanism of FIG. 1;

FIG. 3 is a fragmentary side elevational view generally as seen along line 3-3 in FIG. 2, but with a number of parts omitted for purposes of illustration;

FIG. 4 is a view similar to FIG. 3 but showing certain parts in another operational position; and

FIG. 5 is a schematic diagram of an electric circuit suitable for charging nickel cadmium batteries and incorporating the thermal switch mechanism of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, particularly to FIG. 1, there is shown therein a new and improved thermal switch mechanism 10 suitable for use as a battery charger control and incorporating one form of the present invention.

The thermal switch mechanism 10 includes a base or support 11 formed from a suitable insulating material such as a phenolic resin. A frame 12 of suitable electrically conductive material is securely mounted to the base 11. In the exemplification the frame 12 includes a central portion 13 and a pair of arms 14 and 15, with the arms 14 and 15 extending away from the central portion 13 in generally the same direction. The central portion 13 and the arm 14 are each securely mounted in the base 11 by suitable tabs 16 which project through the base. Thisfixes the central portion 13 and arm 14 relative to the base and relative to each other. The arm 15 is pivotal about the central portion 13 so that its spacing with regard to arm 14 may be adjusted. To this end a portion of material forming the frame 12 may be removed at the junction of the arm 15 and central portion 13 as indicated by the numeral 17. A flange 18 is formed at the distal end of the arm 14 and is bent generally outwardly away from the arm 15 and includes a central recess or depression 19. Since the distal end having flange 18 is beyond tab 16, the flange 18 may be adjusted as by bending the distal end of arm 14.

A thermal drive means is mounted to the frame 12. In the exemplification the thermal drive means includes a three leg thermal actuator 20 having elongated legs 21, 22 and 23 all of which extend from a plate portion 24. The distal ends of each of the legs 21-23 is attached to the flange 18 by some suitable means such as welding, with the center leg 23 being attached in the depression 19 so that the leg 23 is offset with respect to the legs 21 and 22. Additionally, the legs are attached to the flange 18 with the center leg 23 under tension. With this arrangement the thermal actuator is biased so that the plate portion 24 tends to a position toward the central portion 13 of the frame 12, assuming the legs 21, 22 and 23 are at the same temperature.

The thermal drive means also includes a heater which is selectively energizable for varying the temperature of the central leg 23 with respect to the outside legs 21 and 22. In the exemplification the heater takes the form of an insulated wire 25 which is wrapped about the center leg 23 so as to be in good heat transfer relationship thereto. It will be understood that, if desired, a thin sheet of some suitable electrical insulating material may be placed between the leg 23 and the wire 25 toassure no electrical conduction therebetween. A toggle spring 26 is mounted with one end supported by a tang 27 formed on the plate portion 24 of the thermal actuator and its other end supported in a small opening 28 adjacent the distal end of the arm 15. A movable contact 29 is securely mounted in the plate portion 24 and extends to both sides of the actuator 20. It will be understood that other thermal actuators such as bimetals can be used. However, the three leg actuator of the exemplification is substantially insensitive to variations in ambient temperature.

A first stationary contact 30 is secured to the base 11 by some suitable means such as tabs 31 which extend through a suitable opening in the base and are bent over to engage the opposite side of the base. An ear 32 may be bent up at one end of the contact 30 to form a convenient means for connecting the stationary contact in a suitable electric circuit. The other end of contact 30 is bent upwardly to form an upstanding portion 33 adjacent and generally parallel to the plate portion 24 of the actuator 20. One end of the heater 25 is electrically connected to the upstanding portion 33 by some suitable means such as welding.

A second stationary contact 34 is mounted to the base 1 l by tabs 35 which extend through an opening in the base and are bent over against the other side of the base. The stationary contact 34 includes an upstanding ear 36 by which electrical connection may conveniently be made to the contact. At the other end, the contact is bent upwardly so as to have an up wardly angled intermediate portion 37 and an upstanding portion 38 which is generally parallel to the plate portion 24 of the thermal actuator 20. The upstanding portions 33 and 38 of the stationary contacts are generally in alignment with each other and in alignment with the movable contact 29 and are spaced apart on opposite sides of the thermal actuator 20 from each other.

With the mechanism as thus far described the tension in center leg 23, assuming the three legs 21-23 are at about the same temperature, normally biases the thermal actuator for engagement of the movable contact 29 with the upstanding portion 33 of stationary contact 30. Upon energization of the heater 25, the temperature of center leg 23 rises with respect to the temperature of the outer legs 21 and 22 and the center leg 23 expands so as to relieve the tension in the center leg. This causes the actuator to move toward upstanding portion 38 of stationary contact 34 and the toggle spring 26 imparts a snap action to the movement of the thermal actuator. This disengages movable contact 29 from stationary contact 30 and engages it with stationary contact 34. Upon de-energization of the heater 25, center leg 23 cools and, as the temperature of center leg 23 approaches that of the outer legs, the reverse movement occurs. That is, the actuator is snapped back in the other direction so that movable contact 29 is disengaged from upstanding portion 38 of stationary contact 34 and is moved back to engagement with the upstanding portion 33 of contact 30.

So that the thermal switch mechanism will proceed through a desired sequence of operation and then inactivate itself, there if provided a blocking means having a position normally preventing the engagement of movable contact 29 with stationary contact 30 and movable to a second position allowing engagement of contacts 29 and 30. In the exemplification the blocking means includes a flexible strip 39 of suitable insulation material such as a polyester resin for instance. The strip 39 extends along the upstanding portion 33 of stationary contact 30, through a suitable opening 40 in the base 11 and then along the other side of the base. Its opposite end is trapped in a manual operator or pushbutton 41. The pushbutton 41 is slidably received in the base I l and is biased by a spring 42 so that the pushbutton 41 and strip 39 normally are in the position shown in FIG. 4. In this position the strip 39 extends between the stationary contact 30 and movable contact 29 so as to prevent engagement and an electrical connection therebetween. When it is desired to initiate a cycle of operation of the thermal switch mechanism, the pushbutton is manually moved to the right (as seen in FIGS. 3 and 4). This moves the flexible strip 39 from between the contacts 29 and 30, and the bias on the thermal actuator 20 by the tension in leg 23 immediately causes the actuator to move to the position shown in FIG. 3 with the movable contact 29 engaging the stationary contact 30. Upon release of the pushbutton 41 the strip 39 moves to the position shown in FIG. 3 in which it butts against the movable contact 29 but does not prevent engagement and electrical connection between the movable contact 29 and stationary contact 30. When the heater 25 has been energized a sufiicient period of time that the thermal actuator 20 snaps to its other position, that is with movable contact 29 engaging portion 38 of stationary contact 34, the natural resiliency of the strip 39 causes it to return to the position shown in FIG. 4. Subsequently when the temperature of the thermal actuator 20 returns to equilibrium and it snaps back toward stationary contact 30, the insulating strip is again positioned between the contacts 30 and 29 preventing their engagement and electrical connection.

It will be understood that thermal actuators of the type shown have a temperature differential. That is, there is a difference between the operating temperature, or temperature of the center leg 23 with respect to the outer legs, at which the actuator snaps in one direction, and the operating temperature, or temperature of the center leg 23 with respect to the outer legs, at which the actuator snaps back in the other direction. This differential is controlled by the tension in the toggle spring 26. In the exemplification thermal switch mechanism this temperature is controlled and adjusted by adjusting the position of arm 15 with respect to arm 14. To this end a differential adjust screw 43 is provided. The head 44 of the screw rides against the outside of arm 14, more particularly against the junction between arm 14 and central portion 13 which is a structurally very stable point. From there the screw projects through a suitable opening in the arm 14 and diagonally across the frame 12 where its distal end 45 is threadily received in the boss 46 provided in the arm 15. By suitable adjusting of the differential screw the arm 15 is caused to pivot about its junction with cenn'al portion 13 so that the spacing between the arms 14 and 15 is selectively varied to adjust the tension on the toggle spring 26. This effectively sets a desired temperature differential for the actuator. Similarly the base operating point, that is the temperature of the center leg 23 with respect to the outer legs at which the actuator will snap from its position with contact 29 engaging contact 30 to its position with contact 29 engaging contact 34, may be set by bending the distal end of arm 14. This sets the position of flange 18 and normally is done at the time of manufacture.

In some applications of thermal switch mechanisms, such as use as a control for battery charger for instance, it is desired to provide an additional switch which is normally open and is closed at the beginning of a charging cycle to assure complete discharge of the battery prior to its charging. In the exemplification mechanism such a switch is provided by a flexible strip conductor 47. One end 48 of the conductor extends through and is firmly held in a suitable opening 49 in the base 11. From the end 48 the main portion of the strip conductor 47 extends through a slot 50 provided in the intermediate portion 37 of stationary contact 34 so as to normally be spaced slightly above a tang 51 of the contact 34. Then the strip 47 extends through a slot 52 formed in the insulating strip 39. The conductor 47 may extend under the thermal actuator 20 and adjacent the stationary contact 30 but does not engage either of these elements. When the insulation strip 39 is in its normal position, that is as shown in FIG. 4, the conductor 47 does not engage and thus does not form an electrical connection with the stationary terminal 34. However, when the insulating strip 39 is in its other position (as seen in FIG. 3) one edge of the strip 39 forming the slot 52 engages the conductor 47 and bends it downwardly (as seen in FIG. 1) so that the conductor 47 engages the tang 51 of stationary contact 34. Thus the conductor 47 and stationary contact 34 form a normally open switch which is closed when movable contact 29 engages stationary contact 30.

The end of the insulated wire 25 remote from stationary contact 30 is lead through a suitable opening 53 in the base 1 1 and then is electrically connected to the end 48 of the conductor 47.

Referring now particularly to FIG. 5 there is shown a schematic diagram of an electrical charging circuit for batteries of the nickel cadmium type incorporating a thermal switch mechanism of FIGS. 1-4. It will be understood that with batteries of the nickel cadmium type, there is no deleterious effect incident to completely discharging the batteries; however, overcharging the battery can have deleterious effects including causing the batteryto rupture. The charging circuit includes a step down transformer 55 having a primary 56 which may be connected to a suitable source of electrical energy such as a usual household supply by means of a plug 57. The secondary 58 of the transformer is provided with two end taps 59 and 60, each of which is connected to a conductor 61 through diodes 62 and 63 respectively. The secondary 58 is also provided with a center tap 64 which is connected to a movable switch arm 65. The control also includes a pair of output terminals 66 and 67 which are adapted to be connected to a battery 68 such as a nickel cadmium battery. A normally open switch 69 is electrically connected between the output terminals 66 and 67 and is mechanically interconnected with the insulating strip 39. A heater 70 is connected between the conductor 61 and thus the terminal 66 and a stationary terminal 71.

Relating the circuit diagram of FIG. 5 to thermal switch mechanism the terminal 66 would be the end 48 of conductor 47, the terminal 67 is stationary contact 34, .the stationary terminal 71 is stationary contact 30; the normally open switch 69 is formed by conductor 47 and stationary contact 34; and the movable switch arm 65 is formed by the frame 12 and thermal actuator and movable contact 29, all of which are electrically interconnected. ln constructing a control in accordance with the wiring diagram of FIG. 5 the conductor 61 is connected to the end 48 of conductor 47, which also eifectively connects it to one end of the insulated wire (corresponding to heater 70 of the circuit diagram). The other end of wire 25 is permanently connected to stationary contact which corresponds to stationary terminal 71. The center tap 64 of the transformer is connected to the frame 12 by use of one of the tabs 16, which corresponds to movable switch arm 65. One side of a battery to be charged is connected to the end 48 of conductor 47, which corresponds to terminal 66 and the other end is connected to the stationary contact 34, which corresponds to terminal 67.

Assuming the circuit is connected, including a battery connected to terminals 66 and 67 and the plug 57 inserted in an outlet from a suitable source of electrical energy, nothing happens initially as the insulator 39 prevents engagement of movable switch arm 65 with stationary terminal 71 and normally open switch 69 is open. To start a battery charging sequence the button 41 is moved so as to remove the insulator 39 from between stationary terminal 71 and movable switch arm 65. This allows movable switch arm 65 to engage stationary terminal 71 and closes normally open switch 69. The connection from conductor 61 through heater 70, terminal 71 and switch 65 back to center tap 64 energizes the heater 70. At the same time switch 69 effectively shunts the battery 68 and during the period of heating of the thermal actuator assures that the battery is substantially completely discharged. Subsequently the movable switch arm moves from stationary terminal 71 to stationary terminal 67. This allows strip 39 to return to the position shown in the circuit diagram, opening switch 69. The heater 70 is effectively de-energized and the battery 68 is connected across the transformer from conductor 61 through terminal 66 and then through the terminal 67 and the movable switch arm 65 back to the center tap of the transformer 64. Thus a unidirectional charging voltage is applied to the battery until the movable switch arm 65 is disengaged from the stationary terminal 67. At this time charging of the battery is completed and the thermal switch mechanism is effectively de-energized.

The temperature differential of the thermal actuator is adjusted by means of the differential adjust screw such that the charging time is calibrated to essentially completely charge the battery 68 without providing such an overcharge as to cause any deleterious effect on the battery. It will be understood that, since the charging time of the battery depends on cooling of center leg 23 with respect to the outer legs 21 and 22 and all three legs are exposed to the same ambient temperature, variations in this ambient temperature will not cause a variation in the charging time. Also since the heater is deenergized during the period of time the battery is being charged, the charging time of the battery is independent of any variations in the supply voltage.

While there has been described what at present is considered to be the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various modifications may be made therein without departing from the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A thermal switch mechanism, including:

a. first and second spaced apart stationary contacts;

b. a movable contact biased toward engagement with said first stationary contact and movable to engagement with said second stationary contact;

c. blocking means normally in a first position preventing engagement of said first stationary contact and said movable contact, said blocking means being selectively actuable to a second position. for allowing engagement of said first stationary contact and said movable contact; thermal drive means effective to disengage said movable contact from said first stationary contact and to engage said movable contact with said second stationary contact, said thermal drive means thereafter being effective to disengage said movable contact from said second stationary contact and return said movable contact toward said first stationary contact;

e. said blocking means returning to its first position preventing engagement of said first stationary contact and said movable contact upon said thermal drive means efiecting disengagement of said first stationary contact and said movable contact.

2. A thermal switch mechanism set forth in claim 1 wherein said blocking means includes an electrically insulative member normally positioned between said first stationary contact and said movable contact and manually removable therefrom.

3. A thermal switch mechanism as set forth in claim 2 wherein engagement of said movable contact with said first stationary contact prevents entry of said electrical insulative member therebetween.

4. A thermal switch mechanism as set forth in claim 1 further including a second movable contact positioned for selective engagement with said second stationary contact; said blocking means being interconnected with said second movable contact for effecting separation of said second movable contact and said second stationary contact when said blocking means is in its first position and for effecting engagement of said second movable contact and said second stationary contact when said blocking means is in its second position.

5. A thermal switch mechanism, including:

a. a pair of spaced apart arms extending in generally the same direction;

b. an elongated, thermal responsive actuator mounted on one of said arms and extending toward the other of said arms;

c. toggle means interconnecting said actuator and the other of said arms for providing said actuator with a snap action movement; heating means positioned to cause movement of said actuator in opposite directions in response to selective energization and de-energization of said heating means;

e. a pair of spaced apart stationary contacts, each of said stationary contacts being positioned on a side of said actuator opposite the other of said stationary contacts;

. a movable contact carried by said actuator for engagement with a difierent one of said stationary contacts upon movement of said actuator in opposite directions; and means for selectively adjusting the spacing between said arms for setting the difierential between the operating temperature at which said actuator will snap in one direction and the operating temperature at which said actuator will snap in the other direction.

6, A thermal switch mechanism, including:

a. a pair of spaced apart arms extending in generally the same direction;

b. an elongated, thermal responsive actuator mounted on one of said arms and extending toward the other of said arms;

c. toggle means interconnecting said actuator and the other of said arms for providing said actuator with a snap action movement;

d. heating means positioned to cause movement of said actuator in opposite directions in response to selective energization and de-energization of said heating means;

e. a pair of spaced apart stationary contacts, each of said stationary contacts being positioned on a side of said actuator opposite the other of said stationary contacts;

f. a movable contact having two oppositely facing contact faces and a contact side linking said two contact faces, said movable contact carried by said actuator for engagement of said contact faces with a different one of said stationary contacts upon movement of said actuator in opposite directions; and

g. blocking means for blocking engagement of said movable contact with one of said stationary contacts, said blocking means comprising a strip of electrical insulation slidably mounted upon said one stationary contact and biased to a first position in which first position at least a portion of said strip of electrical insulation is disposed between said movable contact and said one stationary contact, and means for sliding said strip of electrical insulation upon actuation over said one stationary contact to a second position in which second position said strip of electrical insulation portion is disposed from out between said movable contact and said one stationary contact and in which second position said strip of electrical insulation is biased against said movable contact side.

7. A thermal switch mechanism, including:

a. a frame having a central portion and a pair of spaced apart arms, said arms extending from said central portion in generally the same direction, said central portion and one of said arms being fixed, the other of said arms being pivotal about said central portion;

b. an elongated, thermal responsive actuator mounted on one of said arms and extending toward the other of said arms;

c. toggle means interconnecting said actuator and the other of said arms for providing said actuator with a snap action movement;

d. heating means positioned to cause movement of said actuator in opposite directions in response to selective energization and de-energization of said heating means;

e. a pair of spaced apart stationary contacts, each of said stationary contacts being positioned on a side of said actuator opposite the other of said stationary contacts;

f. a movable contact carried by said actuator for engagement with a different one of said stationary contacts upon movement of said actuator in opposite directions; and

g. adjustment means interconnecting between said arms for selectively eiTecting pivotal movement of said other of said arms to set the differential between the temperature at which said actuator will snap in one direction and the temperature at which said actuator will snap in the other direction.

* i it i 

1. A thermal switch mechanism, including: a. first and second spaced apart stationary contacts; b. a movable contact biased toward engagement with said first stationary contact and movable to engagement with said second stationary contact; c. blocking means normally in a first position preventing engagement of said first stationary contact and said movable contact, said blocking means being selectively actuable to a second position for allowing engagement of said first stationary contact and said movable contact; d. thermal drive means effective to disengage said movable contact from said first stationary contact and to engage said movable contact with said second stationary contact, said thermal drive means thereafter being effective to disengage said movable contact from sAid second stationary contact and return said movable contact toward said first stationary contact; e. said blocking means returning to its first position preventing engagement of said first stationary contact and said movable contact upon said thermal drive means effecting disengagement of said first stationary contact and said movable contact.
 2. A thermal switch mechanism set forth in claim 1 wherein said blocking means includes an electrically insulative member normally positioned between said first stationary contact and said movable contact and manually removable therefrom.
 3. A thermal switch mechanism as set forth in claim 2 wherein engagement of said movable contact with said first stationary contact prevents entry of said electrical insulative member therebetween.
 4. A thermal switch mechanism as set forth in claim 1 further including a second movable contact positioned for selective engagement with said second stationary contact; said blocking means being interconnected with said second movable contact for effecting separation of said second movable contact and said second stationary contact when said blocking means is in its first position and for effecting engagement of said second movable contact and said second stationary contact when said blocking means is in its second position.
 5. A thermal switch mechanism, including: a. a pair of spaced apart arms extending in generally the same direction; b. an elongated, thermal responsive actuator mounted on one of said arms and extending toward the other of said arms; c. toggle means interconnecting said actuator and the other of said arms for providing said actuator with a snap action movement; d. heating means positioned to cause movement of said actuator in opposite directions in response to selective energization and de-energization of said heating means; e. a pair of spaced apart stationary contacts, each of said stationary contacts being positioned on a side of said actuator opposite the other of said stationary contacts; f. a movable contact carried by said actuator for engagement with a different one of said stationary contacts upon movement of said actuator in opposite directions; and g. means for selectively adjusting the spacing between said arms for setting the differential between the operating temperature at which said actuator will snap in one direction and the operating temperature at which said actuator will snap in the other direction.
 6. A thermal switch mechanism, including: a. a pair of spaced apart arms extending in generally the same direction; b. an elongated, thermal responsive actuator mounted on one of said arms and extending toward the other of said arms; c. toggle means interconnecting said actuator and the other of said arms for providing said actuator with a snap action movement; d. heating means positioned to cause movement of said actuator in opposite directions in response to selective energization and de-energization of said heating means; e. a pair of spaced apart stationary contacts, each of said stationary contacts being positioned on a side of said actuator opposite the other of said stationary contacts; f. a movable contact having two oppositely facing contact faces and a contact side linking said two contact faces, said movable contact carried by said actuator for engagement of said contact faces with a different one of said stationary contacts upon movement of said actuator in opposite directions; and g. blocking means for blocking engagement of said movable contact with one of said stationary contacts, said blocking means comprising a strip of electrical insulation slidably mounted upon said one stationary contact and biased to a first position in which first position at least a portion of said strip of electrical insulation is disposed between said movable contact and said one stationary contact, and means for sliding said strip of electrical insulation upon actuation over said oNe stationary contact to a second position in which second position said strip of electrical insulation portion is disposed from out between said movable contact and said one stationary contact and in which second position said strip of electrical insulation is biased against said movable contact side.
 7. A thermal switch mechanism, including: a. a frame having a central portion and a pair of spaced apart arms, said arms extending from said central portion in generally the same direction, said central portion and one of said arms being fixed, the other of said arms being pivotal about said central portion; b. an elongated, thermal responsive actuator mounted on one of said arms and extending toward the other of said arms; c. toggle means interconnecting said actuator and the other of said arms for providing said actuator with a snap action movement; d. heating means positioned to cause movement of said actuator in opposite directions in response to selective energization and de-energization of said heating means; e. a pair of spaced apart stationary contacts, each of said stationary contacts being positioned on a side of said actuator opposite the other of said stationary contacts; f. a movable contact carried by said actuator for engagement with a different one of said stationary contacts upon movement of said actuator in opposite directions; and g. adjustment means interconnecting between said arms for selectively effecting pivotal movement of said other of said arms to set the differential between the temperature at which said actuator will snap in one direction and the temperature at which said actuator will snap in the other direction. 